The present invention is directed to an improvement in the method of producing an electrical heating element and fitting assembly of the type disclosed in U.S. Pat. No. 3,657,519 which issued on Apr. 18, 1972 on an application copending with above parent application Ser. No. 194,742.
In the art of electrical heating elements which are used within the sump of either a commercial or a domestic dishwashing machine, commonly the heating element includes an elongated tubular metal sheath in which a nickel-chromium electrical resistance wire is concentrically supported by a thermally conductive electrical insulation material such as magnesium oxide. The ends of the wire are attached to corresponding terminal pins which project axially from the end portions of the sheath. A machined metal fitting is commonly brazed or soldered to the end portions of the sheath.
To protect the dry rigid magnesium oxide insulation material and hermetically seal it against moisture, the material is sandblasted or mechanically removed from each end or tip portion of the sheath to define an annular cavity surrounding the projecting terminal pin. This cavity is then filled with a sealant material such as an epoxy resin, for example, as illustrated in U.S. Pat. No. 3,354,294. These sandblasting and filling operations require substantial time and add significantly to the cost of producing the heating element.
The above patent application discloses a novel and an improved means for securing the end portions of a sheath-type heating element to the wall of a liquid heating tank or vessel. This means includes a tubular bulkhead bushing or fitting which is drawn from sheet metal such as brass and is deformed to define helical convolutions which form external threads for receiving a mating drawn sheet metal nut. The bulkhead fitting is secured and sealed to the corresponding end portion of the sheath by soft solder which forms an electrical ground connection between the end portion of the sheath and the fitting so that the sheath can be grounded through the fitting by a suitable ground wire attached to the fitting through a ring-type terminal.